﻿HOW 
  INSECTS 
  FLY 
  — 
  SNODGEASS 
  

  

  415 
  

  

  feathers. 
  Experimenting 
  in 
  this 
  way 
  with 
  insects 
  of 
  different 
  orders, 
  

   Demoll 
  found 
  that 
  the 
  currents 
  of 
  air 
  drawn 
  toward 
  a 
  stationary 
  insect 
  

   hy 
  the 
  vibrations 
  of 
  its 
  wings 
  come 
  not 
  only 
  from 
  in 
  front, 
  but 
  also 
  

   from 
  above, 
  from 
  the 
  sides, 
  and 
  from 
  below, 
  and 
  that 
  the 
  currents 
  

   given 
  off 
  are 
  all 
  thrown 
  out 
  to 
  the 
  rearward. 
  (Fig. 
  24.) 
  The 
  strength 
  

   of 
  the 
  currents, 
  how- 
  

   ever, 
  is 
  not 
  the 
  same 
  

   from 
  all 
  directions, 
  

   as 
  is 
  indicated 
  by 
  the 
  

   relative 
  thickness 
  of 
  

   the 
  arrows 
  in 
  the 
  

   diagrams. 
  The 
  air 
  

   is 
  drawn 
  toward 
  the 
  

   insect 
  most 
  strongly 
  

   from 
  before 
  and 
  

   above 
  the 
  anterior 
  

   part 
  of 
  the 
  body; 
  

   the 
  outgoing 
  cur- 
  

   rents 
  are 
  strongest 
  

   in 
  a 
  horizontal 
  or 
  

   slightly 
  downward 
  

   direction. 
  Most 
  of 
  

   the 
  oncoming 
  cur- 
  

   rents, 
  therefore, 
  are 
  

   turned 
  to 
  the 
  rear 
  in 
  

   the 
  neighborhood 
  of 
  

   the 
  insect's 
  body, 
  and 
  

   condensed 
  in 
  a 
  small 
  

   region 
  behind 
  it. 
  

  

  If 
  the 
  insect 
  is 
  

   free 
  to 
  move, 
  the 
  

   mechanical 
  effect 
  of 
  

   the 
  vibrating 
  wings 
  

   on 
  the 
  air 
  will 
  be 
  the 
  

   same 
  as 
  when 
  the 
  

   insect 
  is 
  held 
  sta- 
  

   tionary; 
  but, 
  instead 
  

   of 
  moving 
  the 
  air, 
  

   or 
  instead 
  of 
  moving 
  

   the 
  air 
  to 
  the 
  same 
  

   extent 
  as 
  before, 
  the 
  

   greater 
  part 
  of 
  the 
  wing 
  force 
  will 
  propel 
  the 
  insect 
  through 
  the 
  air 
  

   opposite 
  the 
  direction 
  of 
  the 
  air 
  currents 
  created 
  when 
  the 
  insect 
  is 
  

   secured. 
  The 
  fact 
  that 
  the 
  vibrating 
  wings 
  produce 
  air 
  currents 
  does 
  

   not 
  mean 
  that 
  the 
  insect 
  will 
  be 
  carried 
  along 
  on 
  the 
  currents 
  of 
  its 
  

  

  B 
  

  

  Figure 
  24.— 
  Diagrams 
  showing 
  the 
  currents 
  of 
  air 
  created 
  by 
  the 
  vibrat- 
  

   ing 
  wings 
  of 
  an 
  insect 
  held 
  stationary. 
  The 
  thickness 
  of 
  the 
  arrows 
  

   indicates 
  the 
  relative 
  strength 
  of 
  the 
  currents. 
  (From 
  Doinoll, 
  1918.) 
  

   A, 
  Lateral 
  view, 
  showing 
  currents 
  in 
  the 
  median 
  vertica 
  plane; 
  B 
  

   dorsal 
  view, 
  showing 
  currents 
  in 
  the 
  horizontal 
  plane 
  

  

  